My dear Faraday
Having of late been much taken up with researches of a peculiar sort, and obtained results from them which I am vain enough to think not entirely unworthy of your notice I take the liberty to give you a short account of my doings. The phosphorous smell which is developped when electricity (to speak the profane language) is passing from the points of a conductor into air or when lightning happens to fall upon some terrestrial object, or when water is electrolysed, has been engaging my attention the last couple of years and induced me to make many attempts at clearing up that mysterious phenomenon. Though baffled for a long time, at last I think I have have succeeded so far as to have got the clue which will lead to the discovery of the true cause of the smell in question. The facts which refer to that subject are as follows:
1.) The phosphorous smell given off during the electrolysation of water is only disengaged at the positive electrode and no trace of it at the negative one.
2.) The odoriferous principle can be preserved in well closed glass bottles for any length of time.
3.) The disengagement of that smell depends a) upon the nature of the metal constituting the positive electrode b) upon the chemical constitution of the (electrolytic) fluid being placed between the electrodes c) upon the temperature of that fluid. With reference to a) I have to state that of all metals examined by me it is only, gold and platina which do yield the smell. The more readily oxidable metals as well as char‑-coal will not allow the disengagement of that prin‑ciple, even not iron, though this substance when acting the part of the positive electrode resembles so very much the precious metals. As to b) I have found out that the smell is disengaged out of dilute (chemically pure) sulphuric, phosphoric, nitric acid, of aqueous solutions of many salts, and that it is never obtained from common or strong nitric acid, from solutions of protosulphate of iron or any substance having a great affinity for oxigen, from aqueous solutions of chlorides, bromides, jodides, muriatic acid, hydrobromic acid &c. If only a small quantity of nitrous acid, protosulphate of iron, proto‑chloride of iron or of tin be added to dilute sul‑phuric, phosphoric, nitric acid, the disengagement of the odoriferous principle will not take place. With reference to an aqueous solution of potash I have made the curious observation that sometimes it yields the smell, and sometimes it does not; even dilute sulphuric acid exhibits that anomaly, but very rarely. I have not yet been able to ascertain the cause of that phenomenon. With reference to c) I have made out that any electrolytic fluid which is capable of disengaging the phosphorous smell at a moderate temperature will not yield it when heated near its boiling point.
4.) If a comparatively small quantity of powdered charcoal, iron, zinc, tin, lead, antimony, bismuth, arsenic or some drops of mercury are thrown into a bottle containing the odorous principle (received at the positive electrode) the smell will be very quickly, almost instantaneously destroyed. Char-coal powder and iron filings act the most rapidly. The same effect is produced by pouring a small portion of nitrous or common fuming nitric acid or solutions of protosulphate of iron, proto‑chloride of iron or of tin into such a bottle. If platina or gold be brought in a red hot state into the vessel, the smell will also be annihilated.
5.) If platina or gold plate be plunged only for a few seconds into an atmosphere of oxigen gas having been disengaged at the positive electrode and exhibiting the peculiar smell, the metals mentioned will be powerfully polarized in the negative way, just in the same manner as if they had been plunged into the vapours of bromine or chlorine. But to obtain that effect it is necessary that the metals be not covered with moisture. The thinnest film of water surrounding their surface will prevent them from assuming the electro-negative condition. To a very slight degree copper acts like gold or platina. I was not able to polarize zinc, brass, iron.
6.) Gold and platina being heated are incapable of assuming the polar state.
7.) If a piece of platina be polarized in the way before mentioned and afterwards brought for a few moments into an atmosphere of hydrogen the electro-motive power of the metal will be destroyed (if not too long kept in the latter gas). The same effect is obtained by heating the polarized plate.
8.) A polarized stripe of gold or platina plate preserves its voltaic condition for some time in the open air.
9.) The current produced by polarized gold or platina is of a short duration.
10.) Oxigen having been deprived of its odoriferous principle by the means indicated at 4) for instance by char-coal has altogether lost its polarizing power and you may keep platina as long you like within such oxigen, the metal will never acquire any perceptible degree of voltaic polarity.
11.) If a stripe of clean platina or gold plate be held opposite to a blunt point of a metallic rod (which is attached to the first conductor of a well working common electrical machine) at a distance of about an inch or so, few turns of the glass-plate will be sufficient to polarize to a sensible degree the metallic stripe. The voltaic state excited in the metal under these circumstance is the electro-negative one. I made my experiments with a platina plate 1 1/2 inch long and 1/3 of an inch wide; after having alternately exposed the two sides of my plate to the action of the electrical brush (produced at blunt point of the rod) for about 25 seconds I obtained a deviation of 170°. The fluid into which I plunged the plate was water containing 1/9 of sulphuric acid and my galvano‑meter made use of is provided with 2000 and some hundreds coils. Gold acts in the same way as platina does, copper is very slightly polarized under these circumstances but not so zinc, iron and brass; at least I could not succeed to excite in the latter metals that voltaic condition.
12.) Gold or platina are negatively polarized whether being held in the hand or insulated.
13.) The same metals do not assume the polar state if they are attached to the first conductor i.e. if the electricity is made to pass from those metals into the surrounding air.
14. Gold and platina are negatively polarized be [sic] the first conductor charged with positive or negative electricity.
15. If those metals are covered with the thinnest film of moisture they are incapable of being polarised by the electrical brush, neither is the peculiar voltaic condition called forth in them when they are exposed to the action in a heated state.
16. When the point from which the brush issues is heated or wetted cold or dry gold and platina will also not be polarized by the latter (brush).
17. That point being heated or moistened * does not disengage the phosphorous smell.
18.) The brush having been deprived by any means of its peculiar smell has entirely lost its polarizing power.
19. Platina being negatively polarized by common electri‑city loses its electro-motive power when plunged into an atmosphere of hydrogen for a few seconds and the same effect is obtained by heating the metal.
20. In common air the polarized gold or platina preserves its peculiar voltaic state for some hours.
21. The current produced by these (polarized) metals are of so short a duration, that they may be considered as instantaneous:
It seems to me that the above mentioned facts allow some important conclusions to he drawn from and a series of conjectures to be founded upon. Allow me to mention some of them.
a) The peculiar smell produced by lightning, common electricity and the voltaic current is due to some particular gazeous body.
b) The voltaic and chemical bearings of that body are very similar to those of chlorine and bromine.
c) Water, atmospheric air and perhaps all sorts of matter do contain an electrolyte whose anion is the odoriferous principle in question and whose cation is most likely hydrogen.
d)That electrolyte is decomposed by lightning, common electricity and the voltaic current and its odoriferous anion liberated.
e)The polarizing or electromotive power of that anion is resulting from its great tendency to unite with the hydrogen of water &c. It acts in that respect like chlorine or bromine.
f)The chemical affinity of the odoriferous substance for other bodies is such as to surpass with respect to intensity that of most, perhaps of all what they call electro‑-negative elements.
g)The electrolyte spoken of being present in water and atmospheric air it is probable that that compound acts an important part in the house hold of nature and it is not unlikely that its workings are closely connected with the more general electrical phenomena of our globe.
My first Idea was that the smell in question might be due to a compound being produced at the positive electrode by some secondary action, but the whole body of facts above‑-mentioned are to my opinion not favorable to such a view. To raise my conclusions and conjectures to undoubtful certainty, the supposed elementary substance must be obtained pure and in an insulated state. The beautiful voltaic arrangement of our Friend's Mr. Grove1 can alone make us arrive at that end and I shall write to him in order to engage his attention to that subject. What I have communicated to you, is as you will easily perceive a very rough and imperfect sketch of the results of my late researches. The subject is far from being exhausted and requires a good deal more of experimental investigation. I hardly want to tell you that I am working night and day to get deeper into the mine a[nd] nearer to its hidden treasures. In the report I have to lay before the british association next autumn a detailed account of my investigations will be given and I hope it will be such as to be considered as not being quite void of scientific interest2.
If you should think the contents of my letter important enough as to merit the attention of the royal Society3 or the royal Institution you are entirely at liberty to communicate them to those learned bodies. I have not yet made them known in any continental journal or to any society except to our philosophical society at Bâle.
The other day I saw in Galignani's Sunday Observer a very imperfect account of your last paper read before the royal Society on the source of current-electricity4. Some of your proofs for the truth of the chemical theory of Galvanism were mentioned and to my opinion they are such as to leave no doubt about the subject. But I am afraid the philosophers of the north will hear no reason, and find out some new piece of sophistry in order to keep up their favorite hypothesis.
Our friend Grove wrote me the other day communicating to me some very interesting results of his late researches with which you are no doubt acquainted5. What do you think about the fact that the transfer or oxidation of particles in the voltaic arc is definite for a definite current? Important as such a fact is I cannot yet understand it that is to say I cannot conceive that by the simple oxidation of the positive electrode the current can be conducted in the same way as by electrolysis both actions being so very different from each other.
From Mr. Grove's letter I also learned to my infinite regret that you are not yet enjoying perfect health.
My dear Faraday allow me to repeat my former request and permit me to readvise you not to overwork yourself and to manage a little your mental and physical forces, for your health and life are most precious to your friends in particular and to the scientific world at large. We cannot yet spare you and you must continue to be our leader for many years to come. But to have our wishes accomplished and our hopes realized you ought to listen a little to the entreaties of your friends and to grant to your mind and body some rest. I am sure Mrs. Faraday will be of my opinion and confident she will not cease reminding you of it.
Pray remember me most friendly to your Lady and let me have before long good tidings from you.
Believe me, my dear Faraday | Your's faithfully | C.F. Schoenbein
Bâle April 4th 1840.
* The best way to destroy the electrical smell or rather to prevent its appearance is to envelop the blunt point with a piece of linen impregnated with distilled water.
Address: Dr. M. Faraday | &c &c &c | Royal Institution | London
FARADAY, Michael (1840b): “Experimental Researches in Electricity. - Seventeenth Series. On the source of power in the voltaic pile.- (Continued)”, Phil. Trans., 130: 93-127.
GROVE, William Robert (1840): “On some Phaenomena of the Voltaic disruptive Discharge”, Phil. Mag., 16: 478-82.
SCHOENBEIN, Christian Friedrich (1840): “An Account of Researches in Electro-Chemistry”, Rep. Brit. Ass., 209-20.
Please cite as “Faraday1259,” in Ɛpsilon: The Michael Faraday Collection accessed on 28 April 2024, https://epsilon.ac.uk/view/faraday/letters/Faraday1259